The Arctic tundra has been shown to be a potentially significant regional sink for methyl chloride (CH 3 Cl) and methyl bromide (CH 3 Br), although prior field studies were spatially and temporally limited, and did not include gross flux measurements. Here we compare net and gross CH 3 Cl and CH 3 Br fluxes in the northern coastal plain and continental interior. As expected, both regions were net sinks for CH 3 Cl and CH 3 Br. Gross uptake rates (À793 nmol CH 3 Cl m À2 day À1 and À20.3 nmol CH 3 Br m À2 day À1 ) were 20-240% greater than net fluxes, suggesting that the Arctic is an even greater sink than previously believed. Hydrology was the principal regulator of methyl halide flux, with an overall trend towards increasing methyl halide uptake with decreasing soil moisture. Water table depth was one of the best predictors of net and gross uptake, with uptake increasing proportionately with water table depth. In drier areas, gross uptake was very high, averaging À1201 nmol CH 3 Cl m À2 day À1 and À34.9 nmol CH 3 Br m À2 day À1 ; in flooded areas, gross uptake was significantly lower, averaging À61 nmol CH 3 Cl m À2 day À1 and À2.3 nmol CH 3 Br m À2 day À1 . Net and gross uptake was greater in the continental interior than in the northern coastal plain, presumably due to drier inland conditions. Within certain microtopographic features (low-and high-centered polygons), uptake rates were positively correlated with soil temperature, indicating that temperature played a secondary role in methyl halide uptake. Incubations suggested that the inverse relationship between water content and methyl halide uptake was the result of mass transfer limitation in saturated soils, rather than because of reduced microbial activity under anaerobic conditions. These findings have potential regional significance, as the Arctic is expected to become warmer and drier due to anthropogenic climate forcing, potentially enhancing the Arctic sink for CH 3 Cl and CH 3 Br.

Evaluating the ecological impact of an oil spill is a complex issue requiring coherently articulated examination of the sequence of interactions that link the cell, where contaminants exert their effects, to the ecosystem, where interactions with human activities arise. This sequence of interactions traverses the frontiers between scientific disciplines (chemistry, toxicology, physiology, and fisheries ecology). Using the common sole (Solea solea L.) as a model species for the coastal habitats polluted by the "Erika" oil spill, our research project attempted to define indices of functional integrity that characterised the consequences of fuel exposure at the different biological levels. The coupling of field observations with experimental laboratory work revealed how functional alterations which are readily observable within individuals and their organs are progressively obscured as investigation progresses towards more complex organisational levels. Some of the approaches and indices are proposed as instruments for evaluating the impact of contamination by hydrocarbons.

[1] Coastal salt marshes are sources of CH 3 Br and CH 3 Cl to the atmosphere, but the wide range of reported emission rates illustrates the need to understand better the factors controlling net fluxes. Here we demonstrate the use of a stable isotope tracer method to separately evaluate gross production and consumption fluxes to determine their relative roles in the overall net flux. At two salt marshes in northern California, gross production exceeds gross consumption at all measured sites, leading to a large net source overall. Emission rates are within the range observed at other temperate salt marshes. By evaluating the consumption component separately, we explain how a typical salt marsh source might convert into a temporary net sink by exposing the ecosystem to uncharacteristically high concentrations of methyl halides. This circumstance may account for the reported net uptake of methyl chloride during the growing season at a coastal salt marsh in China. Citation: Rhew, R., and O. Mazéas (2010), Gross production exceeds gross consumption of methyl halides in northern California salt marshes, Geophys. Res. Lett., 37, L18813,

An analytical method consisting in enzymatic deconjugation, solid phase extraction and purification, and gas chromatography/mass spectrometry analysis after derivatization was used in this study to quantify Polycyclic Aromatic Hydrocarbon (PAH) metabolites in the bile of fish. The method has been applied in a laboratory experiment studying the fate of pyrene in basin containing soles. This study has allowed the identification of 1-hydroxypyrene as the single metabolite in bile after enzymatic deconjugation. In a second time, 1-hydroxypyrene has been used as a biomarker of exposure in the case of the "Erika" oil spill. This biomonitoring was successful in demonstrating the exposure of juvenile soles to PAHs present in the "Erika" fuel oil.